Septicemia causes substantial morbidity and mortality among patients in the United States, with a rising burden of Staphylococcus aureus infection. Although blood cultures are the diagnostic gold standard for blood stream infection (BSI), sensitivity is limited and results are not rapidly available. Such diagnostic delays can extend the time to administration of effective antibiotics, which is an independent risk factor for mortality. Conversely, diagnostic uncertainty also leads to high rates of empiric overtreatment, fueling the burden of antimicrobial resistance. Thus, novel approaches that are faster and more accurate are needed to differentiate between the major pathogens causing sepsis and BSI.
Whereas conventional diagnostic approaches have focused on identifying the infecting pathogen, a growing body of evidence suggests that the host's inflammatory response to the pathogen also represents a potential diagnostic tool. In vitro and In vivo experiments have revealed fundamental differences in host response to Gram-positive and Gram-negative bacterial infection, including significant differences in Toll-like receptor (TLR) signaling and cytokine production. Distinctive gene expression profiles exist for viral, bacterial, and fungal infections in both animal model systems and ex vivo stimulation of human peripheral blood leukocytes. Peripheral blood mononuclear cell (PBMC) gene expression signatures have also been evaluated in humans for a variety of conditions including severe infection, bacterial vs. viral illness, systemic lupus erythematosus, atherosclerosis, and radiation exposure. Taken together, these studies provide strong evidence that global changes in host blood gene expression patterns can be used to differentiate disease states.
Staphylococcus aureus causes a spectrum of human infection. Diagnostic delays and uncertainty lead to treatment delays and inappropriate antibiotic use. Early diagnostic strategies for S. aureus BSI could improve patient care by reducing the time required to establish the diagnosis and provide appropriate treatment while avoiding unnecessary anti-MRSA antibiotics. There is a need in the art to have alternative methods for diagnosing and treating patients with bacterial infection, such as sepsis.